In the aforesaid U.S. Pat. No. 3,918,083, there is disclosed a planar integrated circuit with bilateral switching capability. More particularly, the circuit comprises four vertical transistors having a common collector, with four emitter-base leads between adjacent pairs of transistors. The effective circuit is a lateral triac comprising eight transistors in a novel transistor bridge construction, and having all active junctions reaching a single surface. Because of its symmetrical construction, either a light-generated photocurrent or a gate current applied across one of two gate terminals and an associated main terminal, may be used to trigger the device and control an ac circuit. With the particular two-stage base diffusion disclosed in U.S. Pat. No. 3,920,493, issued Nov. 18, 1975, and assigned to the same assignee as the instant application, ac line voltages of 120 volts RMS may be controlled. Because devices of the type described are, effectively, planar, photosensitive triacs, we have named them "photracs".
Historically, high-power semiconductive devices have been large, discrete devices with junctions reaching a passivated edge rather than a major surface. The patent of Blicher et al, U.S. Pat. No. 3,427,515 may be considered representative of many in this area.
The present invention represents a combination of planar and mesa technologies, one which carries the voltage capabilities of the purely planar photrac into the 400 volt range.